P8210016

This shows the path of the bypass port. With the thermostat closed, water does not exit out the top, instead, it gets routed down the smaller hole in the restrictor plate orifice where it exits the front cover as shown. At the water pump, this location leads into the suction side of the water pump. So you can see, if a totally open thermostat does not cover the restrictor plate properly, you will continue to get hot coolant recirculated right back into the block.